[ARC5] Selectivity ratings of ARC-5 receivers.

[Leslie Smith]

  Hello Ken,
  I'll be a goose and make a public fool of myself.
  Dad always said, "Remember son, there's no bigger fool than a public
  fool."
  The units of measurement 2x and 1000x are voltage (measured with a
  volt-meter or CRO or similar meter)

  I understand 1 "S" unit equals 6 dB - and in my view this is too
  small.  

  "My thinking (your thinking) is that in order to achieve a 3bD
  increase in signal level at the receiver the transmitter [output
  power] must be doubled"
  That's correct, assuming your unit of measurement is power.
  But at the receiver your unit of measurement is voltage.
  dB = 20log(E2/E1)  so 20log(1000/1) is 20 * 3 = 60
  For a 50% increase in voltage level 20 * log (2/1) = 20 * 0.3010 =
  6dB.

  Sorry to be long winded


  73 de Les Smith
  vk2bcu at operamail.com


On Tue, Oct 29, 2013, at 14:31, Kenneth G. Gordon wrote:
> Reading the ARC-5 maintenance manual, I see that the selectivity for,
> say, 
> the R-26 (3 - 6 MHz) receiver is listed at 7.3 Kc at 2X, and 26 Kc at
> 1000X.
> 
> Now 1000X is 60 db, but isn't 2X 3db and not 6db?
> 
> Color me confused at this point.
> 
> My thinking is that in order to achieve a 3db increase in signal level at
> the 
> receiver, the transmitter must be doubled in output power, given
> identical 
> conditions.
> 
> Or am I all wet here?
> 
> Ken W7EKB
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